Information

Information

Example of use of the frozen values





Faults can be intermittent, which is important to remember when fault-tracing for possible causes. If the fault is not present when the vehicle is in the workshop, a fault cause can be missed as the values can be correct when fault-tracing is carried out. A good indication of when the fault occurred the first time are the frozen values that can be read out using VIDA/Details.
The frozen values are stored immediately after a fault has been detected. Most parameters in the frozen values are the same for all faults and indicates a general status when a fault has been detected, e.g. engine speed, load, coolant temperature, vehicle speed and battery voltage. Some of them have been selected to give a better understanding of the specific fault. Diagnostic Trouble Code (DTC) ECM-903F Throttle position (TP) can be used as an example of how the frozen values can be used (this is only one example and there may be deviations in reality).
One of the checks given in fault-tracing is "voltage supply to throttle unit" and continues with a suggestion to check the battery and charging system. However, the battery's condition, with the vehicle in the workshop, does not show the battery voltage when the fault was detected. The best information is in the frozen values, i.e. the voltage that the Engine control module (ECM) detected, when the Electronic throttle module (ETM) indicated the fault.
However, remember that this is not an indication of the voltage supply to the Electronic throttle module (ETM), but to the Engine control module (ECM). If the Engine control module (ECM), according to the frozen values, had a good voltage, the battery worked. The voltage supply to the Electronic throttle module (ETM) should therefore be checked separately.





In this case, we assume that the vehicle had a low battery voltage in the workshop. As seen in the frozen values however, the battery voltage was correct when the fault occurred, and this was therefore probably not the cause. This is an example of how the frozen values can be used, to make fault-tracing more efficient and prevent taking too much time fault-tracing incorrectly. This prevents fault-tracing and correcting a fault that was not actually the cause of the problem, which was originally to be solved.
The odometer setting (km) is included among the frozen values in the Engine control module (ECM). This makes a fast comparison with the odometer counter possible, so that one can determine if the fault occurred as part of the fault-tracing and can be ignored.
For example, the CAN related diagnostic Trouble Codes (DTCs) can be detected when the battery voltage drops when working on the vehicle, by the passenger compartment lighting and other loads draining the battery. The frozen values indicate the odometer setting in km. Multiplying this value by 0.62 gives the distance in miles. The current distance in miles and km can be read out using VIDA.
The following should be taken into account when using frozen values for fault-tracing. The frozen values, that should be used with care, are those that have been stored for CAN and are related to Diagnostic Trouble Codes (DTCs) for the Electronic throttle module (ETM).
If the Electronic throttle module (ETM) detects that the communication to the Engine control module (ECM) is interrupted, error flags are stored in the Electronic throttle module (ETM). These error flags are sent to the Engine control module (ECM) as soon as communication on the CAN is working again. This means that the Engine control module (ECM) stores the Diagnostic Trouble Codes (DTCs) as soon as the Electronic throttle module (ETM) supplies them.
This, in turn means that it is at this time that the frozen values are stored. For the Electronic throttle module (ETM) this means that the frozen values occur from a point in time after the fault first occurred.